1. Field of the Invention
The present invention relates to an electrostatic capacitance type input device. In addition, the present invention relates to a calculation method for calculating an approach position of a conductor.
2. Description of the Related Art
FIGS. 34 and 35 show an example of an input device as an example of the related art of the present invention. FIG. 35 is an overhead view taken along line XXXV-XXXV of FIG. 34. An input device 9X shown in these drawings composes a touch panel by being used by superimposing with a liquid crystal display panel 9Y. This touch panel is used as display means and operating means of, for example, a cell phone 9Z. An example of a touch panel of the related art is disclosed in Japanese Patent Application Laid-Open No. 2008-33777.
The input device 9X is provided with a transmission plate 91 (omitted from FIG. 35), a transmission plate 92, detection electrodes 9a and 9b, wiring 931, wiring 932 (omitted from FIG. 34), a flexible substrate 971 and an IC chip 972. The detection electrodes 9a and 9b are respectively formed on the transmission plates 91 and 92. The detection electrodes 9a each extend along the y direction. The detection electrodes 9b each extend along the x direction. The wiring 931 is connected to the detection electrodes 9a. The wiring 932 is connected to the detection electrodes 9b. 
FIG. 36 schematically shows the detection electrodes 9a connected to the IC chip 972. The IC chip 972 is provided with a plurality of input terminals 979. Each of the input terminal's 979 is individually connected to the wiring 931. Although not shown in the drawing, this applies similarly to the detection electrodes 9b. 
As shown in FIG. 34, the cell phone 9Z has a transparent cover 98. The input device 9X is joined to the transparent cover 98. When a user operates the cell phone 9Z, a conductor 9D such as a finger approaches or contacts the transparent cover 98, thereby causing electrostatic capacitance to be generated between the conductor 9D and the detection electrodes 9a and 9b. FIG. 37 indicates a graph representing values corresponding to changes in electrostatic capacitance between the conductor 9D and the detection electrodes 9a when the conductor 9D has approached or contacted the transparent cover 98. The position where the conductor 9D has approached the transparent cover 98 can be detected by specifying the detection electrode 9a connected to the input terminal 979 in which electrostatic capacitance has increased.
In the input device 9X, electrostatic capacitance of the detection electrodes 9a and the detection electrodes 9b may vary slightly due to the effects of external noise even if the conductor 9D has not approached the transparent cover 98. Consequently, the IC chip 972 determines whether or not an increase in electrostatic capacitance of the detection electrodes 9a and the detection electrodes 9b exceeds a prescribed threshold value either before or after obtaining information relating to the approach position of the conductor 9D in the x direction and y direction. In the case the increase in electrostatic capacitance of the detection electrodes 9a does not exceed the specified threshold value, the IC chip 972 determines that the conductor 9D is not approaching the detection electrodes 9a and the detection electrodes 9b. At this time, the IC chip 972 outputs a signal to the outside indicating that the conductor 9D is not approaching. On the other hand, in the case the increase in electrostatic capacitance of the detection electrodes 9a and the detection electrodes 9b exceeds the prescribed threshold value, the IC chip 972 outputs information to the outside relating to the approach position of the conductor 9D.
However, in the case the transparent cover 98 of the cell phone 9Z is thick, for example, the minimum separation distance between the conductor 9D and the detection electrodes 9a and the detection electrodes 9b increases. Whereupon, an increase in electrostatic capacitance of the detection electrodes 9a and the detection electrodes 9b decreases even if the conductor 9D approaches. Consequently, there is no alternative but to decrease the above-mentioned threshold value. If the threshold value is decreased, there is the risk of an increase in electrostatic capacitance of the detection electrodes 9a and the detection electrodes 9b exceeding the threshold value in the case electrostatic capacitance of the detection electrodes 9a and the detection electrodes 9b has changed due to the effects of external noise. This leads to the problem of the conductor 9D being determined to have approached the detection electrodes 9a and the detection electrodes 9b despite the conductor 9D not actually approaching the detection electrodes 9a and the detection electrodes 9b. 